1 lecture #9 – animal nutrition and digestion. 2 key concepts: animals are heterotrophic!...

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Lecture #9 – Animal Nutrition and Digestion

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Key Concepts:

• Animals are heterotrophic!• Nutritional needs – what animals get from

food• Food processing• The human digestive system

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Critical Thinking

• Is this animal approaching the fruit or the flower???

• Why???

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Critical Thinking

• Is this animal approaching the fruit or the flower???

• Why???

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Animals are always consumers

• Only photosynthesis can convert solar energy to usable chemical energy

• Plants store chemical energy• Animals eat plants (or other animals)• ….of course this is somewhat simplified….

but NO animals are autotrophic

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Critical Thinking

• Why do we eat??? Specifically, what do we get from food???

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Critical Thinking

• Why do we eat??? Specifically, what do we get from food???

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Why we eat – energy

• Animals generate ATP by aerobic respiration

• Main substrate is carbohydratesFats are also usedProteins are used as a “last resort”

• Digestion converts consumed polymers to the monomers used in respiration

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Diagram – bioenergetics and the fate of food

Remember bioenergetics

• Managing the energy budget is essential to maintaining animal function

• ATP powers basal metabolism, other activities; maintains homeostasis; etc…

• Animals must eat to make ATP

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Why we eat – carbon skeletons

• Animals need organic carbon scaffolds to build our own organic molecules – such as???

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Why we eat – carbon skeletons

• Animals need organic carbon scaffolds to build our own organic molecules – such as

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Why we eat – essential nutrients

• Molecules that animals cannot make at allDo not have the right biosynthetic pathways

• Must be eaten in pre-assembled form• Some common to all animals; some

specializedEssential amino acidsEssential fatty acidsVitaminsMinerals

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Essential Amino Acids

• Most animals use the same 20 amino acids to make what???

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Essential Amino Acids

• Most animals use the same 20 amino acids to make

• Most animals can only synthesize about half

• Remaining amino acids must be consumedAll animal proteins are complete – contain all

the essential amino acidsAll plant proteins are incomplete – missing

some of the essential amino acids

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Chart – essential amino acids; overlap between grains and legumes

Human vegetarian diets must mix plant groups to obtain all essential amino acids

Grains and legumes mixed provide all essential amino acids – cultural traditions prevent protein deficiencies

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Essential Fatty Acids• Some unsaturated fatty acids cannot be

synthesized• Most animals (especially humans!) get

adequate essential fatty acids from their diet

• We use fatty acids for????

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Essential Fatty Acids

• Some unsaturated fatty acids cannot be synthesized

• Most animals (especially humans!) get adequate essential fatty acids from their diet

• We use fatty acids for

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Vitamins• Organic molecules used in small quantities• Water soluble vitamins usually function as

coenzymes• Fat soluble vitamins function in nutrient

absorption, as antioxidants, etc..• Deficiencies are rare with an adequate,

balanced diet

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Critical Thinking

• Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why???

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Critical Thinking

• Which category of vitamin is more likely to accumulate and become toxic – water soluble or fat soluble??? Why???

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Table – essential vitamins; sources and functions

Study table in

textfor a

general under-

standing

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Minerals

• Inorganic elementsSome required in small amounts; some in

largerRequirements vary by taxon

• Many different functionsSome metabolic; some structural

• Know top 8 minerals and their main functions

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Mineral Functions???

• Calcium – • Phosphorous – • Sulfur – • Potassium – • Chlorine – • Sodium – • Magnesium –• Iron –

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Some Mineral Functions

• Calcium –• Phosphorous –• Sulfur –• Potassium –• Chlorine –• Sodium –• Magnesium –• Iron –

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Diagram – food procession in a small mammal

Food Processing• Ingestion• Digestion

• Absorption

• Elimination

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Evolution of Compartmentalization

• Food digestion must be containedWhy???

• Earliest containment structures are food vacuolesSponges digest entirely intra-cellularly

• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one

openingMore complex animals have a digestive tube with an

opening for ingestion and one for elimination

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Evolution of Compartmentalization

• Food digestion must be contained• Earliest containment structures are food

vacuolesSponges digest entirely intra-cellularly

• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one

openingMore complex animals have a digestive tube with an

opening for ingestion and one for elimination

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Evolution of Compartmentalization

• Food digestion must be contained• Earliest containment structures are food

vacuolesSponges digest entirely intra-cellularly

• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one

openingMore complex animals have a digestive tube with an

opening for ingestion and one for elimination

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Diagram – sponges and their choanocytes

Sponges digest food in vacuoles that fuse with lysosomes containing hydrolytic enzymes

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Evolution of Compartmentalization

• Food digestion must be contained• Earliest containment structures are food

vacuolesSponges digest entirely intra-cellularly

• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one

openingMore complex animals have a digestive tube with an

opening for ingestion and one for elimination

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Images – a jellyfish and a flatwormDiagram – two cell layers in cnidarians

Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles

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Jellies and flatworms start digestion in gastrovascular cavities; finish in food vacuoles

Problem???

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Evolution of Compartmentalization• Food digestion must be contained• Earliest containment structures are food

vacuolesSponges digest entirely intra-cellularly

• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one

opening –More complex animals have a digestive tube with an

opening for ingestion and one for elimination

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Hands On

• Be sure to examine specimens and comment on structure-function relationships

• Be sure to examine Cnidarians at the aquarium and comment on structure-function relationships

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Evolution of Compartmentalization

• Food digestion must be containedAvoids digestion of body cells and tissues

• Earliest containment structures are food vacuolesSponges digest entirely intra-cellularly

• Most animals digest at least partly outside the cellsSimplest body plans have a digestive sac with one

openingMore complex animals have a digestive tube with an

opening for ingestion and one for elimination

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Critical Thinking

• The 2-hole tube body plan processes food sequentially – no mixing of incoming food and outgoing waste

• Can you think of another advantage for the 2-hole tube plan???

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Two hole tube digestive plan – essentially an open tube that passes through the body

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Critical Thinking

• The 2-hole tube body plan processes food sequentially – no mixing of incoming food and outgoing waste

• Can you think of another advantage for the 2-hole tube plan???

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Diagram – development of specialization in 2-hole tubular digestive tracts in earthworms, insects and birds

Tubular system allows for specialization and

efficiency

• Specialization based on habitat and diet

• Both divergent and convergent patterns have emergedAll mammals have a cecumBoth earthworms and birds

have developed crops

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Schematic diagram – the human digestive system

The Human Digestive System

• Relatively straightforward adaptations to an omnivorous diet

• Tube running from mouth to anus with specialized regions for food processing, absorption, and elimination of wastes

• Accessory glands supply lubrication, digestive enzymes and other secretions

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Diagram – the human digestive tract

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Diagram – the oral cavity, pharynx and esophagus; same diagram on next two slides

Oral cavity, pharynx and esophagus allow for chewing and swallowing food

• Teeth cut and grind• Tongue mixes and

pushes bolus to back• Saliva lubricates

food, protects the mouth lining, buffers pH, kills bacteria, and begins the digestion of carbohydrates

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Diagram – specifically the function of the epiglottis

Oral cavity, pharynx and esophagus allow for chewing and swallowing food

• Epiglottis tips down to direct food from pharynx to esophagus (so you don’t breathe your food)

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Oral cavity, pharynx and esophagus allow for chewing and swallowing food

• Peristaltic contractions in esophagus push food to stomach

• Food does not fall by gravity – remember our quadruped ancestors…

• Sphincter (ring) muscles also control passage of food

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Stomach continues the action…

• Stores food (very folded and stretchy)• Muscle contractions mix food• Lining secretes gastric juice

Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria

Pepsin begins protein hydrolysisStomach lining protected from self-digestion by

thick mucus and secretion of inactive pepsin precursor

• Controls passage of food into small intestine

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Stomach continues the action…

• Stores food (very folded and stretchy)• Muscle contractions mix food• Lining secretes gastric juice

Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria

Pepsin begins protein hydrolysisStomach lining protected from self-digestion by

thick mucus and secretion of inactive pepsin precursor

• Controls passage of food into small intestine

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Diagram – the somach lining and secreting cells

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Ulcers…..• Stomach lining replaces itself by mitosis

about every 3 days• Lesions still sometimes occur• Ulcer risk factors???

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Ulcers…..• Stomach lining replaces itself by mitosis

about every 3 days• Lesions still sometimes occur• Ulcer risk factors

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Other animals can get ulcers, too

• From a student’s extra credit • Causes include stress, diet, genetic

abnormalities, microbial infections, very finely ground grains, heredity, bile reflux that destroys stomach lining

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Stomach continues the action…

• Stores food (very folded and stretchy)• Muscle contractions mix food• Lining secretes gastric juice

Very acidic (pH ~2) hydrochloric acid dissolves cell matrices and denatures proteins in swallowed food; also kills many ingested bacteria

Pepsin begins protein hydrolysisStomach lining protected from self-digestion by

thick mucus and secretion of inactive pepsin precursor

• Controls passage of food into small intestine

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Diagram – the cells lining the stomach, secretion of digestive juices

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The Small Intestine• Completes digestion and absorbs monomers

Some absorption occurs in other parts of the digestive tract, but most in the SI

• More than 6m long• Multiple levels of folding increase SA• Surface area about 600m2!!• Most digestion occurs in the first 25cm of the

small intestineEnzymatic hydrolysis

• Most absorption occurs in the latter 5.75m of the small intestine

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Diagram – the human small intestine

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Diagram – levels of folding in the human small intestine

Four levels of folding function to increase surface area – tube,

interior folds, villi, microvilli

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Increased surface area, especially of transport epithelia, is a hallmark of large, complex,

multi-dimensional animals

Factoids from humans:• Lungs have 100 m2 of surface area (almost 1/2

as big as room)• Small intestine has surface area of a tennis

court• 80 km of tubules in a single kidney• 100,000 km of blood vessels = almost 3X

circumference of earth

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The Small Intestine• Completes digestion and absorbs monomers

Some absorption occurs in other parts of the digestive tract, but most in the SI

• More than 6m long• Multiple levels of folding increase SA• Surface area about 600m2!!• Most digestion occurs in the first 25cm of the

small intestineEnzymatic hydrolysis

• Most absorption occurs in the latter 5.75m of the small intestine

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Diagram – the pancreas, liver and gall bladder; structure and function

Pancreas secretes enzymes and bicarbonate; liver secretes bile

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Chart – digestive enzymes; point of secretion and substrate; same on next slide

Digestive enzymes and substrates

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Most digestion in duodenum (1st 25cm)

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The Small Intestine• Completes digestion and absorbs monomers

Some absorption occurs in other parts of the digestive tract, but most in the SI

• More than 6m long• Multiple levels of folding increase SA• Surface area about 600m2!!• Most digestion occurs in the first 25cm of the

small intestineEnzymatic hydrolysis

• Most absorption occurs in the latter 5.75m of the small intestine

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Diagram – close-up of villi and microvilli

Monomers cross into epithelial cells, then into interstitial fluid, then into the lymph or

bloodstream

• Some transport is facilitated, some active

• Each villus includes lymph and blood vessels

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Diagram – fat digestion process; same next slide

Fat Digestion

• Fats are hydrophobic• Bile salts emulsify large

fat droplets into smaller droplets more surface area

• Lipase digestion produces fatty acids and mono-glycerides

• These monomers form into micelles

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Fat Absorbtion• Micelles are tiny enough to

diffuse into epithelial cells• Monomers are recombined

into fats in the epithelial cells

• Fats mix with cholesterol and are coated with proteins

• Resulting globules are transported into the lymph, and eventually into the blood (at shoulder ducts)

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Diagram – how blood vessels absorb nutrients; same next slide

Intestinal blood vessels drain directly into the hepatic portal vein

• Nutrients get sent straight to the liver for metabolic processing

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Intestinal blood vessels drain directly into the hepatic portal vein

• From the liver, the blood goes straight to the heart for distribution throughout the body

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Diagram – circulation patterns in humans showing relationship between circulation and major organs

Critical Thinking

• Where will the levels of blood sugar and other nutrients vary the most???

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Critical Thinking

• Where will the levels of blood sugar and other nutrients vary the most???

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The large intestine, AKA the colon

• Connected to SI at T junction• Dead-end of T is the cecum• Appendix extends off cecum

Cecum functions as fermentation chamber in many animals, especially herbivores

Human cecum is small, relatively functionlessAppendix contributes to immune function, but

is dispensable Appendix may function to repopulate intestines with

beneficial bacteria after intestinal infections

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Diagrams – the cecum in omnivores (humans) vs. specialized herbivores (koalas)

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The large intestine, AKA the colon

• Remainder of LI is ~ 1.5m• Main function is to absorb water

7l of fluid is secreted into intestinal lumenAdditional water is consumed in dietSI and LI together absorb ~ 90% Inflammation of LI reduces water absorption diarrhea

• LI also houses both commensal and mutualistic bacteriaLive on undigested or unabsorbed materialsProduce important vitamins (K, B’s, folic acid, biotin)Some produce stinky gasses as a byproduct of metabolism

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The large intestine, AKA the colon

• Final section of LI is the rectum• Feces are produced as water is absorbed from

waste organic materialsWaste includes LOTS of bacteria; cellulose40% of the dry weight of feces is bacteria

• Feces are stored in the rectum• When the “time” comes, feces are eliminated

through the anusSphincter muscles control eliminationOne is voluntary, one involuntarySome, but not complete control over defecation

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Diagram – the human digestive tract with the large intestine highlighted

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Diet is a selection pressure• Dentition

Different tooth shapes for ripping and grinding• Length of small intestine

Herbivores typically have much longer SI• Other compartments and symbioses

Fermentation chambers that house micro-organisms that can digest cellulose (animals lack cellulases)

Enlarged ceca (first feces are re-eaten)Esophageal pouches (crops in some birds, the

“stomachs” of ruminants)

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Critical Thinking

• How might diet affect tooth evolution?• Carnivores – • Herbivores – • Omnivores –

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Critical Thinking

• How might diet affect tooth evolution?• Carnivores –• Herbivores –• Omnivores –

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Diagram – differences in tooth structure

Ripping, crushing and shredding teeth

Biting and grinding teeth

Combo of teeth for biting, tearing, grinding and crushing

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Diet is a selection pressure• Dentition

Different tooth shapes for ripping and grinding• Length of small intestine

Herbivores typically have much longer SI• Other compartments and symbioses

Fermentation chambers that house micro-organisms that can digest cellulose (animals lack cellulases)

Enlarged ceca (first feces are re-eaten)Esophageal pouches (crops in some birds, the

“stomachs” of ruminants)

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Diagram – differences in the digestive tract of carnivore vs. herbivore

Most plant material is tough and

fibrous – the longer

digestive tract in herbivores allows more

time and space for

digestion and absorption of both nutrients

and water

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Cecum in magenta…..

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Diet is a selection pressure• Dentition

Different tooth shapes for ripping and grinding• Length of small intestine

Herbivores typically have much longer SI• Other compartments and symbioses

Fermentation chambers that house micro-organisms that can digest cellulose (animals lack cellulases)

Enlarged ceca (first feces are re-eaten)Esophageal pouches (crops in some birds, the

“stomachs” of ruminants)

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Diagram – the digestive system of a cow

Extra compartments house symbiotic micro-organisms – food is often

regurgitated and / or re-consumed

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Review – Key Concepts:

• Animals are heterotrophic!• Nutritional needs

EnergyCarbon skeletonsEssential nutrients

• Food processing• The human digestive system• Diet as a selection pressure

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Hands On

• Begin your careful dissection of the rat• Follow instructions in lab manual• Answer questions on lab handout• Be careful, delicate and precise!!!!